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PROJECT DESCRIPTION:
HAAT -- the ``Humacao-Arecibo Astrometric Telescope'' -- is a radio telescope planned to fill
two separate, yet complementary, roles in a long-term collaborative partnership between the
UPR-Humacao and the Arecibo Observatory. These are:
(1) To provide a unique research and teaching facility for the University of Puerto Rico
(Humacao Campus), allowing them to exploit the facilities of the Arecibo Observatory of NAIC
(an NSF-funded national center for research.) In this guise HAAT would serve as an instrument
with which students and staff at UPR (Humacao) and other Puerto Rican universities can develop
skills in physics, astronomy, electronics, and computing. This would apply from the classroom,
through the teaching and research laboratories, to use of the facilities of NAIC for full-scale
research projects. Puerto Ricans are significantly under-represented among the nation's scientists
and engineers, and the availability of a significant-sized radio telescope, plus the collaboration of
a leading national radio astronomy center, to the University of Puerto Rico's (UPR) teaching and
research facilities would provide a remarkable opportunity to ``kick-start'' activities to train
Puerto-Rican students in skills fitting them for important roles in science, engineering and
management.
(2) NAIC itself can see the potential for occasional use of just such an instrument as HAAT
towards its own National Center user research program, which is open to all scientists of the
U.S.A. and elsewhere. Thus, NAIC's involvement in the development of HAAT as a cuttingedge
research instrument would be both a contribution from it to the training of Puerto Rican scientists
and engineers, and to enhancing the options it offers to its user base for astronomy, planetary
physics and aeronomy.
SCIENTIFIC IMPACT OF HAAT:
[Note to Murray: This section may need to be shortened further – the points I tried to
get across are, AO, VLBI, phase referencing, and the 11.3 m antenna soon to be
brought to AO ]
The 305-m Arecibo radio telescope is the world's largest, most sensitive, single-dish radio
telescope. It is used to carry out observations in radio astronomy, planetary physics, and the
atmospheric sciences, and is equipped with receivers between 47 MHz and 10 GHz. In addition
to its single-dish capabilities, the Arecibo 305-m radio telescope also participates in Very Long
Baseline Interferometry (VLBI) observations with the VLBA, HSA, EVN and Global VLBI
networks. At present, all observing time on the 305-m telescope is granted on a highly
competitive peer review process, open to the researchers world wide. Although not unknown,
opportunities for undergraduates to utilize it, or indeed gaining hands-on experience in radio
sciences by building equipment for it has been limited.
In order to broaden the range of scientific possibilities it offers its users, while enhancing the
educational and outreach facilities of the Observatory, NAIC is currently in the process of
acquiring an auxiliary 11.3-m radio telescope located nearby. Such an instrument would have
scientific capabilities that are both complementary to, and independent of, the 305-m telescope,
and it would be made available for educational programs in partnership with Puerto Rican
educational institutions as described in this proposal. We foresee the antenna being scheduled in
support of Arecibo user operations with the 305-m telescope for a maximum of ~10 % of its
time. All other time (apart from maintenance) would be available for integration into the
educational and research needs of UPR, and Public Outreach ventures in collaboration with the
UPR and the Observatory's Visitor Center.
Below, we detail some of the specific scientific and education activities that can benefit from this
auxiliary telescope, HAAT. The following scientific directions will form the basis of a
partnership between UPR, led by its Humacao campus, and NAIC/Arecibo Observatory.
VLBI -- Phase Referencing:
Phase referencing in Very Long Baseline Interferometry (VLBI) observations has made it
possible to study very weak radio sources by increasing the effective coherence time for them
from, at maximum, a few minutes to hours (Wrobel et al. VLBA Sci. Memo 24). Currently, some
50 % of VLBI observations are carried out using the phase-referencing technique.
However, phase referencing observations encounter limitations with the Arecibo 305-m
telescope. The Gregorian dome, located on a suspended platform, and sustained by cables, has
slow slew rates (24o/min in azimuth, 2o.4 /min in zenith angle.) Hence, in a typical nodding-style,
phase-referenced observation, where the calibrator could be located 3o or more from the target, a
significant amount of observing time, often ≥ 50 %, is wasted slewing between the two sources,
leading to a significant loss in signal-to-noise ratio. However, phased-referenced VLBI
observations could be performed using the small telescope in which, this ``auxiliary'' telescope
tracks the phase calibrator, while the 305-m antenna observes the target most of the time, and the
Effects due to inospheric phase fluctuations can be derived from the data coming from the small
telescope and applied to the target data from the 305-m dish.
A number of frequency bands below 10 GHz would be required on the auxiliary antenna, these
being those used as standards by the VLBI community. While a separate VLBI backend and
recorder may be required for the auxiliary antenna, it might be possible to time-share a single
system, as is also envisaged for the maser time/frequency standard.
The 11.3-m HAAT antenna:
In searching for an economical solution to obtaining an ``auxiliary'' antenna at Arecibo for use in
phase-referenced VLBI (and other roles) and to be operated in partnership by UPR~(Humacao)
and NAIC, we recently learned that NASA/Canberra Deep Space Communication Complex
(CDSCC) had moth-balled their 11.3-m antenna (DSS-33), earlier used as a HALCA/VSOP
earth station, and were looking for somebody who would be interested in taking over the dish.
This indeed looks a potentially acceptable option for the auxiliary dish, and we have expressed
our interest to NASA and are actively pursuing acquisition. Below we summarize its expected
performance figures.
Effective Area, Aperture Efficiency & Sensitivity
This effective area yields a point-source sensitivity of 0.023 K/Jy. The similar values for
aperture efficiency at X and Ku bands suggest that the antenna will work well to at least a
frequency of 15 GHz, meaning that it will operate efficiently across the complete frequency
range of the 305-m telescope (327~MHz to 10~GHz).
With a system temperature of T deg K, this would give a system equivalent flux density (SEFD)
of 43.5 T Jy. For a system temperature of 25-30 K, this gives an SEFD of 1090-1300 Jy,
compared with an SEFD of about 310 Jy at 5 GHz for a VLBA antenna.
Is HAAT Large Enough to Provide Adequate VLBI Phase Referencing?
If HAAT were to have a similar Tsys to a VLBA telescope at this wavelength, then the baseline
sensitivity for an 11-m to a VLBA antenna (1-) should be ~22 mJy/beam. This implies that, at
the 5-) level, sources brighter than about 110mJy/beam should be suitable for phase
referencing. This would include the majority of sources from the various sections of the VLBA
Calibrator Survey.
RESEARCH & EDUCATIONAL PROGRAM:
The educational program will be developed under two categories:
One for the under graduate students in applied physics in which the students will spend a .... (xxx
months) of internship at the observatory working on hardware/software projects in designing
and building equipment for the HAAT. These students will be mentored jointly by the engineers
of the observatory and the UPR professors.
In the second program, the students in physics and astronomy program of the UPR will join in
the research collaborations undertaken by UPR faculty and NAIC staff astronomers as described
below. The HAAT could also form a laboratory tool for hands-on astronomy technique courses
adopted at the university.
[Note to Murray: The two paragraphs above need further development with more specific
information about the degree, credits, etc. in consultation with Rafael et al.]
Research Area-I : Astronomical Projects using Phase Referencing VLBI
Collaborators: Rafael Muller (UPR-HUMACAO), Juan Carlos Cersocimo (UPR-HUMACAO),
Mayra Lebron (UPR-Rio Piedras), Chris Salter (NAIC-AO), Tapasi Ghosh (NAIC-AO), Jim Cordes
(Cornell University), Paulo Freire (NAIC-AO), Mikael Lerner (NAIC-AO), Robert Minchin
(NAIC-AO)
Stellar (radio/optical) Astrometry:
In a white paper submitted to the NSF ExoPlanet Task Force, Bower et al. (arXiv:astroph/0704.0238v1) explore the possibility of ``Radio Astrometric Detection and Characterization
of Extra-Solar Planets". Utilizing the better than 100-microarcsec positional accuracy routinely
achieved with the VLBA, they propose carrying out a Radio Interferometric Planet search
(RIPL) that will survey 29 low-mass, active (radio-loud) M-dwarf stars over 3 years. This would
have sub-Jovian planet mass sensitivity at distances of about 1~AU from the star.
They also note that, ``Radio astrometric planet searches occupy a unique volume in planet
discovery and characterization parameter space. The parameter space of astrometric searches
gives greater sensitivity to planets at large radii than do radial velocity searches. For the VLBA
and the expanded VLBA, the targets of radio astrometric surveys are by necessity nearby, lowmass, active stars, which cannot be studied efficiently through the radial velocity method,
coronography, or optical interferometry.''
Current measurement errors are limited by the number of nearby compact sources that are well
above the detection threshold of their observations and which can be used as reference sources in
their differential measurements. The addition of Arecibo in such surveys would increase the
detection sensitivity by a factor of four, making it possible to venture into the study of objects
with one third of the mass of Jupiter as companions of similar stellar types. As Arecibo's
primary beam is much smaller than other telescopes, and the slew rate slower, the availability of
HAAT for phase referencing would be highly beneficial for taking such studies down to
thermally emitting stars.
A Broad-impact VLBI Measurement of Trigonometric Parallax of Star Clusters:
In an impressive work using the VLBA at 8 GHz, Menten et al. (2007, A&A, 474, 515) have
determined the trigonometric parallax of several stars in the Orion BN/KL region. This has
allowed them to derive the most accurate value so far ($414\pm 7$~pc) for the distance to this
region, about an order of magnitude better than the previous value of 361$^{+168}_{-87}$~pc
determined from the optical parallax measurement of a single star in this complex by Hipparcos.
Luminosity-based distance estimates of star-forming regions could be adversely affected
by poorly known extinctions, and the new radio technique of Menten et al. is an important way
to improve the estimation of distances, and hence luminosities, with subsequent impact on starformation theories.
As in the previous case, the inclusion of Arecibo would permit the extension of such studies to
fainter, more distant, star-forming regions.
Pulsar Astrometry:
High-precision astrometry of pulsars over multiple epochs can provide their basic astrometric
parameters: positions, proper motions, and annual trigonometric parallaxes. Due to the weakness
of most pulsars, with duty cycles of typically < 10 %, the participation of Arecibo and phase
referencing is often vital to the success of this exercise.
In respect of positional measurements, it is to be noted that VLBI estimations are tied to the
reference frame of the distant quasars, rather than the Solar-system frame provided by pulsar
timing positional estimates. This allows fundamental reference frame ties between the Solarsystem and extragalactic (ICRF) frames via measurements of recycled pulsars, which are highly
stable rotators.
Proper motion estimates allow pulsars to be traced back to their birth sites and, for very young
pulsars, associations with progenitor supernova remnants (SNRs) can be established, providing
an independent age estimate for the remnant. Combined with pulsar distance estimates, proper
motion measurements lead to estimates of space velocities, allowing a study of the natal kicks
imparted to pulsars at the time of their birth.
When a parallax measurement is possible, this yields a model independent estimate for the
distance (and hence velocity) of the neutron star. Such measurements, (i) calibrate models of the
Galactic electron distribution, (ii) constrain SN core collapse using the velocity estimates, and (c)
for hot neutron stars with optically observed thermal surface radiation, provide the photospheric
size and
thus constrain the equation of state of matter at extreme pressures and densities.
Detection Experiemnts:
Present-day VLBI offers thehighest sensitivity radio astronomical observations yet achieved,
with
noise levels approaching 1 $\mu$Jy/beam being attained with arrays using the world's most
sensitive telescopes, and in particular the Arecibo 305-m dish. Hence, the 305-m telescope is
being increasingly used in experiments to detect very weak, very compact, astronomical targets,
such as radio emission from X-ray stars, distant supernovae and their remnants, Gamma-Ray
Bursts, and red-dwarf and other stars. However, for these sensitivity levels to be reached for
targets of very low intensity, it is essential that the observations use phase-referencing.
VLBI imaging of molecular gas in ULIRGs:
In a program of complementary observations at the Arecibo 305-m telescopes and the GBT, a cmwavelength search for prebiotic molecules in Ultraluminous infrared galaxies have been initiated
recently. The project has been inspired by the recent Arecibo detection of the prebiotic molecule,
methanimine (CH2NH) in the protypical ULIRG, and megamaser galaxy, ARP 220 (Salter et al. 2008).
These galaxies are considered to be extreme merger systems and are often heavily obscured at optical
wavelengths. Molecular lines in these galaxies often show wide velocity widths, which often causes line
Blending due to spatial and velocity overlaps. Detailed studies of these objects require phase-referencing
VLBI observations. Sources with positive detection of cm-wave transitions of large molecular species
(prebiotic or otherwise) in the above mentioned AR-GBT search will be followed up in high resolution
mapping using the VLBI arrays and the small-antenna as a phase-referencing unit.
Research Area-II : Using HAAT As An Independent Single Dish
Collaborators: Juan Carlos Cersocimo (UPR-Humacao), Chris Salter (NAIC-AO)
[Note to Bob Brown/Murray:. This section needs shortening + the equations need to be translated
into doc format. I am really out of time, could either of you please do it ? Otherwise, I will fix
this section when I come back.]
Full-Stokes Galactic Plane continuum Surevy with HAAT:
The 11.3-m HAAT telescope, together with existing Arecibo backends, will enable the making
of full-Stokes continuum surveys using the cooled dual-channel receivers that will be built for
use with the dish.
Full-Stokes continuum surveys of the wider Galactic plane at high frequencies using HAAT
would provide unique databases in a number of ways. Firstly, they would yield full spatial
frequency mapping at a number of previously unmapped wavelengths, with competitive
resolution for such extended features as the Galactic background emission, HII complexes, and
middle-aged and old SNRs. Comparison with the existing lower frequency surveys would allow
accurate estimation of the spectral index distribution over these features, providing the ability to
perform accurate thermal-nonthermal separation on angular scales between 1deg. and < 10
arcmin. This would allow the study of energy injection to the ISM and energy losses of
relativistic particles associated with SNRs, and the mechanisms of vertical transport and
diffusion of energy from the disk of the Galaxy into the halo and intergalactic space.
Simultaneously recorded linear polarization measurements are of especial importance. The
appearance of the polarized sky at wavelengths > 21 cm is complex. Westerbork at 327 MHz for
high Galactic latitudes and the Canadian Galactic Plane Survey at 1.4 GHz have shown that there
is little relationship between total intensity and polarization structures. In fact, for the diffuse
Galactic synchrotron emission, the bulk of the area of the Galactic Plane imaged on arcminute
scales at L-band reveals highly structured polarization features with no counterparts in Stokes I.
The accepted interpretation of this is that although the Galactic synchrotron emission is
intrinsically quite smooth, differential Faraday rotation in the intervening magneto-ionic
medium, (the Faraday Screen), imposes fine structure on the polarized emission. In other words,
the
low-frequency polarized sky is dominated by propagation effects rather than by intrinsic
emission structure. This field of study is now moving from phenomenology to astrophysics.
The signals produced by the Faraday Screen are rather weak, and the limited surface brightness
sensitivity of interferometers samples only the strongest. Even for these, the derived rotation
measures (RMs) are noisy due to low signal-to-noise per channel. Moreover, the lack of zero-
spacings in interferometric observations leads to complications in interpretation. The high
brightness sensitivity of HAAT, coupled with afew arcminute beam size at high frequencies,
promises major advances in the study of the magneto-ionic medium. At these frequencies(
\gapp~10~GHz) the effects of Faraday rotation become tiny ($\Delta\theta \propto \nu^{-2}$)
and HAAT can measure linear polarization whose position angles are essentially those intrinsic
to the emission. These can provide both intrinsic directions of magnetic fields, and a database
against which the lower frequency polarization distributions can be definitively interpreted.
In previous studies of the Faraday Screen, the spectral signatures of the polarized intensity have
been examined to seek only a single RM value per image pixel. Such a value corresponds to a
RM in the foreground of the dominant polarized emission component along a given sight-line.
However, the Faraday Screen is spread out in depth along each line of sight, with different
regions of polarized emission at different distances along the sight-line contributing to the
observed spectrum with their corresponding foreground Faraday rotation signature. Because of
depolarization effects, bandwidth integrated polarization will show a lower degree of
polarization than that intrinsic to individual slabs. With an appropriate combination of observing
frequency, bandwidth and spectral resolution, it should be possible to perform Faraday
tomography, wherein the spectral polarized intensity modulations along a given sight-line can be
transformed to a set of polarized intensities as a function of Faraday depth (i.e. RM). Thus, it
should be possible to derive a polarized-intensity data cube (quite like a spectral-line data cube)
with two dimensions being the
sky coordinates and the third being RM. High-frequency images from HAAT would be
invaluable in pursuing this endeavor.
Away from the Galactic plane, the high latitude regions contain several well-known non-thermal
emission structures. Most notable is the North Polar Spur (Loop 1), an object that contains rich
small-scale structure, both on its main arc and in internal ridging. Above b = 45 deg, even low
resolution Dwingeloo measurements have shown this nearby ($\sim$100 pc distant), old SNR to
be > 70\% linearly polarized at 1.4~GHz. HAAT images at a few cm wavelength would directly
reveal magnetic field directions in this object whose RMs are low.
We should specifically mention the L-band Arecibo GALFA Continuum Transit Survey
(GALFACTS), which is being made by an international consortium of astronomers led by Prof.
Russ Taylor (U. Calgary). This full-Stokes survey of the whole sky observable with the 305-m
telescope, covers the frequency range of 1225 -- 1525~MHz, with 8192 frequency channels to
study both the total-intensity and polarized distribution of the celestial radiation. At L-band, the
effect of Faraday rotation on the linearly polarized radiation is considerable, the GALFACTS
precursor surveys demonstrating complex structure both spatially and in frequency. A continuum
survey at much higher frequency, but similar resolution (HPBW $\sim$ 4 arcmin for
GALFACTS), would be invaluable when combined with GALFACTS both to allow thermalnonthermal separation, and to aid Faraday tomography of the linear polarization data. The same
situation exists in respect of that part of the Southern Galactic Plane Survey, an L-band
continuum survey being made with the Parkes radio telescope in Australia (HPBW $\sim$ 15
arcmin; Haverkorn et al 2006). HAAT surveys would also provide the vital low-spatial
frequency data for future interferometric full-Stokessurveys.
Synergy with GLAST
The main processes producing -rays in our Galaxy are believed to be, a) brehmsstrahlung from
the interaction of cosmic-ray electrons and the interstellar gas, and b) the decay of neutral pions
produced in interactions between the gas and cosmic-ray protons and heavier nuclei. The former
is thought to dominate at < 1~MeV, and the latter at energies higher than this. Similar
distributions of $\gamma$-rays are found at low latitudes in both energy ranges, suggesting that
the cosmic-ray heavy particle-to-electron ratio is constant over the
Galaxy. If so, the -ray emissivity, $\eta_{\gamma}$, is proportional to the product of the
cosmic-ray intensity and the $total$ (i.e. neutral and ionized atomic gas, plus molecular gas) gas
density ($\rho$);
\begin{equation}
\eta_{\gamma} \propto N_{0}\rho
\end{equation}
where the cosmic-ray energy distribution is,
\begin{equation}
N(E)dE = N_{0}E^{-\Gamma}dE
\end{equation}
Now, for the synchrotron component of the Galactic radio emission, the
emissivity is,
\begin{equation}
\eta_{R} \propto N_{0}B_{\perp}\!\!^{(\Gamma +1)/2}
\end{equation}
where $B_{\perp}$ is the magnetic field strength perpendicular to the
line of sight.
The Galactic distributions of the three quantities, $N_{0}$, $\rho$ and $B$, are all of
considerable astrophysical interest. Arecibo can contribute significantly to a knowledge of $\rho$
over the accessible sky as the GALFA consortium will provide, a) the 2-dimensional distribution
of HI, while the thermal-nonthermal separation of the continuum emission mapped by the HAAT
and GALFACTS continuum surveys will provide the 2-D distributions of b) the thermal
emission from HII and c) the non-thermal synchrotron emission. The 2-D distribution of the
molecular gas is already available from CO surveys of similar resolution. Hence, combining
Arecibo HAAT and ALFA work with other radio data and the high-fidelity GLAST $\gamma$ray background images
will provide the necessary information to ``unfold'' the 2-D distributions and derive the Galactic
distributions of $N_{0}$, $\rho$ and $B$. This would represent a major contribution to our
understanding of the detailed distribution of the magnetic field and cosmic rays in
the disk of our Galaxy.
Pulsar timing:
Collaborators: ?? (UPR-Humacao), Paulo ?? (NAIC-AO)
(If this is required, Paulo should be asked to expand it.)
The majority of pulsars are too weak to be satisfactorily timed with
an 11-m dish. However, timing observations of the strong Crab and Vela
pulsars would complement dedicated measurements being made to detect
timing glitches in these objects (e.g. Lyne et al., 1996, Nature,
381, 497 \& Lyne et al., 1993, MNRAS, 265, 1003). The signals received
can be piped back to the control room for processing with existing
Arecibo backends.
Research Area-III : Astronomical Projects using the 305-m telescope
Collaborators: Carmen Pantoja (UPR- Rio Piedras), Mayra Lebron (UPR- Rio Piedras), Robert
Minchin (NAIC-AO)
1. ZOA science goals (or some part of ALFAALFA project, ----- text to be develope
2. Radio Recombination line survey
EDUCATION AND OUTREACH PROGRAM
Collaborators:
As a semi-dedicated instrument for the research and education needs of Puerto Rican
universities, an integrated program of teaching, technical development and research will be
developed around HAAT between a Puerto Rican Astronomy Consortium (PRAC), and the
NAIC. As a radio telescope, HAAT would be available for observations 24 hours per day,
subject only to routine maintenance constraints.
On installation of the telescope, a considerable number of engineering and software tasks would
need to be accomplished to bring HAAT on-line, offering excellent experience for students of
the scientific, electronics and computing departments of PRAC institutions. Receivers need to be
constructed, the drive system and other software developed, and remote
operations
implemented, the latter being essential for the classroom utilization of HAAT, the performance
of extended thesis projects, and for the use of HAAT in ``hands-on'' public outreach sessions
coordinated by the UPR and the Arecibo Observatory's ``Angel Ramos Foundation'' Visitor
Center. Observatory staff would be available as a valuable resource to the faculties of PRAC
institutions in terms of research projects centered on HAAT, lecture courses centered around
HAAT-related topics, co-supervision of student research, and participation of Puerto-Rican
students in the Arecibo REU and other summer-student programs. Projects using HAAT could
also be incorporated in the annual RET program for Puerto Rican science teachers run by the
Visitor Center.
Presently, Puerto Rico offers only very limited access to local astronomical instruments for
education, training and research. The high annual humidity, the hurricane season, and the
elevated annual rainfall all mitigate against significant optical facilities being placed on the
island. However, centimeter/decimeter radio observations placed on the island. However,
centimeter/decimeter radio observations are largely unaffected by weather conditions (hurricane
passages apart!) In addition, the presence of both HAAT and the Arecibo 305-m radio telescope,
the world's largest single radio telescope, on the island will represent a truly unique opportunity
for an expansion of astronomical activities within the island's universities that could help
transform a community of 4 million under-represented U.S. Citizens into the academic envy of
many other parts of the nation!
BROADER IMPACT OF THE PROPOSED PROJECT
HAAT as an Independent VLBI Element
HAAT could be a very useful instrument in its own right for VLBI support, especially as it will
have ``full sky coverage''. For many experiments, this would complement the N-S baseline
between LA and PT, by providing an E-W baseline of similar length between itself and the SC
VLBA antenna. HAAT could be used when the 305-m telescope was either not available, not
needed (stronger targets, or those needing greater uv-coverage than the 305-m can provide), or
otherwise inappropriate (e.g. declinations not covered by the 305-m dish.)
Geodetic VLBI
The ``International VLBI Service for Geodesy \& Astrometry'' (IVS) recently laid down a set of
guide lines for the next-generation of geodetic VLBI measurements of station positions and earth
orientation parameters. These are called ``VLBI\,2010''.The aim is to achieve 1~mm positional
accuracy on intercontinental baselines with a 24-hr turnaround for results. However, there is
insufficient funding for an international network at present, and the geodetic community is
interested in any telescope that could participate. As is being planned for HAAT, the antenna
needs to have minimal horizon obstruction, and be sited on good bed-rock.
The VLBI\,2010 requirements specify a telescope design of 12 meter diameter, close to the size
of HAAT, with a system temperature of about T$_{\rm{R}} = 45$\,K (SEFD $<$2500~Jy. A
frequency coverage of 2 - 18~GHz will ultimately be needed, a range that can be covered by
HAAT. Dual-frequency operations are a requirement to allow for ionospheric correction. An
eventual data recording rate of 8 - 16 Gbps is being set as a goal, and is consistent with NAIC
development plans for its VLBI backend; Recording at a rate of 4~Gbps was recently made with
the 305-m telescope using a borrowed digital backend, and dual state-of-the-art Mk5 recorders.
Much of the data transfer is envisaged as being over the internet (e-transfer), and Arecibo is
already the leading player in N. American astronomical eVLBI.
Arecibo would be attractive as it is situated on the Caribbean techtonic plate. This plate is very
complicated, and accurate measurements of velocities in a global frame are most valuable.
Currently, the 25-m VLBA antenna on St. Croix is available to the geodetic array, but only on
occasions per year. For each geodetic session, the geodetic community would need 24 hr
participation. The minimum involvement required is once per month, though once per week
would be welcomed. While the geodetic community intend extending their frequency coverage
to Ka band eventually, this would not be necessary for some while. They would require 2-bit
recording, and early recoding rates of (say) 2 Gbps.
To participate in geodetic VLBI a cable-delay system (i.e. A ``round-trip' phase measurement)
will be needed as system delays need to be tracked at the mm-level. Diurnal effects should be
monitored, and the receiver has be as stable as possible. A dual-frequency GPS receivers should
exist close to the antenna, as is already the case for the planned HAAT site. Geodetic operations
are the responsibility of the individual antennas. Analysis centers exist around the World, with
some being based at universities. It is likely that UPR could become involved? We note that
the analysis of VLBI data is simple compared to that for GPS data. Further, while GPS is good
for measuring regional motions (over $\sim$1000 km), VLBI can provide the tie to more distant
points with better accuracy than GPS
MANAGEMENT PLAN